<!DOCTYPE html>
<title>Imperative Slot API: fallback should be cleared after slot assignment</title>
<link rel="author" href="mailto:xiaochengh@chromium.org">
<link rel="help" href="https://bugs.chromium.org/p/chromium/issues/detail?id=1292292">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<div>
  <div id="host1"><span></span></div>
  <div id="host2"><span></span></div>
</div>

<script>
test(() => {
  const host = document.getElementById('host1');
  const shadow = host.attachShadow({mode: 'open', slotAssignment: 'manual'});
  shadow.innerHTML = '<slot>fallback</slot>';
  host.offsetHeight; // Force layout
  const slot = shadow.firstChild;
  slot.assign(host.firstChild);
  assert_array_equals(slot.assignedNodes(), [host.firstChild]);
  assert_equals(host.offsetHeight, 0, 'Fallback content should not be rendered');
}, 'Text node fallback should be cleared in a subsequently layout');

test(() => {
  const host = document.getElementById('host2');
  const shadow = host.attachShadow({mode: 'open', slotAssignment: 'manual'});
  shadow.innerHTML = '<slot><span>fallback</span></slot>';
  host.offsetHeight; // Force layout
  const slot = shadow.firstChild;
  slot.assign(host.firstChild);
  assert_array_equals(slot.assignedNodes(), [host.firstChild]);
  assert_equals(host.offsetHeight, 0, 'Fallback content should not be rendered');
}, 'Element fallback should be cleared in a subsequent layout');
</script>
